Between April 18th and 22nd, the U.S. Food and Drug Administration assayed 297 samples of fluid milk, cottage cheese, cream and yogurt obtained at retail in 17 states. The samples represented products processed at 132 dairies in 38 states.
No live H5N1 virus was detected in any of the samples that were all pasteurized.
The FDA detected RNA associated with H5N1 in 20 percent of the retail milk samples suggesting widespread infection among dairy herds. To date, USDA-APHIS has recorded more than 50 infected herds in nine states. There is evidence that the infection has been present in dairy herds since late December 2023. Investigations have demonstrated that the bovine udder contains sialic acid receptors for both avian and mammalian strain viruses and also that H5N1 can replicate in udder tissue.
The surveys conducted by FDA on milk correspond to recovery of H5N1 virus in wastewater in areas with known infection among dairy herds.
Bovine influenza is essentially a work in progress and intensive epidemiologic investigations are needed to establish the prevalence rate, modes of transmission and ultimately, measures to control and prevent the infection in this industry. Above all, epidemiologic investigations and characterization of the virus are necessary to ascertain any possible mutations that could potentially result in a zoonotic strain.